Applicant claims priority under 35 U.S.C. xc2xa7119 of German Application No. 198 38 536.6 filed Aug. 25, 1998. Applicant also claims priority under 35 U.S.C. xc2xa7365 of PCT/EP99/06109 filed Aug. 20, 1999. The international application under PCT article 21(2) was not published in English.
1. Field of the Invention
The invention relates to a device and a method for creating one or a plurality of magnetic field gradients through a current conductor that is straight in the site where the magnetic field is measured.
The one or the plurality of magnetic field gradients so created are to be used preferably for the potential-free measurement of the current in the addressed conductor, which is preferably straight in the site where the magnetic field is measured.
2. The Prior Art
It is known to measure currents potential-free by recording their magnetic field with the help of the Hall-effect (Proceedings PCIM Hong Kong, October 1997, pages 129 ff). However, the Hall-transducers commercially available at the present time require relatively expensive and, especially when higher currents are measured, also voluminous iron or ferrite cores for concentrating the magnetic flux in the areas of the respective transducer that are sensitive to the magnetic field (FIG. 1).
Said circumstance, which has to be ascribed to the low magnetic field-sensitivity of the commercially available Hall-transducers mentioned above, has led to the development of more sensitive Hall-converters and other equipment for measuring magnetic fields.
For example, devices are known in the field of Hall transducers or Hall sensors that contain on a silicon substrate of the size of only a few square millimeters both a layer sensitive to magnetic fields, and also flux concentrators [EPFL/Sentron, Highly Sensitive Hall Sensor, shown at the Hannover Messe Industrie (Hannover Industrial Exposition, 1998); and H. BLANCHARD ET AL, Cylindrical Hall Device, Proc. International Electron Devices Meeting (IEDM) 1996), San Francisco, USA, Dec. 8-11, 1996].
Furthermore, a whole series of other methods exists for measuring the magnetic field, which, by virtue of their sensitivity, are suitable for pot potential-free current measurements without iron or ferrite cores as well.
For example, devices for measuring the magnetic field are known since a longer time that operate on the basis of magnetoresistive effects such as the anisotropic magnetoresistive effect (AMR) (Magnetoresistive Sensors III, Final Report of the Combined Project IMOMAG, BMFT Promotion ID 13 MV 0109-0120, chapter 6.1, Magnetic Field Sensor with Integrated Compensation Line MSK 6), or such as the gigantic magnetoresistive effect (GMR) (Magnetoresistive Sensors IV, Symposium and Status Seminar held on Mar. 11 and 12, 1997, in Wetzlar, chapter xe2x80x9cMR Sensors with Giant Resistance Materials: Potencies and Problemsxe2x80x9d).
Furthermore, it seems to be conceivable also in the future to produce such sensor systems on the basis of the colossal magnetoresistive effect (CMR)(loc.cit. page 7 f).
However, all sensor systems possessing a magnetic sensitivity that permits them to measure currents potential-free without the use of voluminous iron cores, have in common that they have high sensitivity to interference fields. Said circumstance is counteracted at the present time, for example in that by arranging the magnetoresistive materials employed in the respective measuring device in a special way, magnetic field gradiometers are produced that have a lower sensitivity to homogeneous fields of interference.
For example, DE 43 00 605 C2 describes a sensor chip that functions especially on the basis of the anisotropic magnetoresistance effect (AMR). Said sensor chip is capable of measuring current potential-free by recording the magnetic field gradient. Devices are also known, of course, that operate based on the GMR effect (Magnetoresistive Sensors IV, symposium and Status Seminar on Mar. 11 and 12, 1997, in Wetzlar, chapter xe2x80x9cMR Sensors with Giant Resistance Materials: Potencies and Problemsxe2x80x9d, page 4 ff) or other magnetic field-sensitive effects, such devices being devised as gradiometers.
The devices introduced above, and also the particularly sensitive Hall sensors with integrated soft-magnetic flux concentrators (EPFL/Sentron, Highly Sensitive Hall Sensor, shown at the Hannover Industrial Exposition in 1998) can be basically devised as gradiometers as well. It is only necessary for said purpose to apply, for example two magnetic field-sensitive surfaces on a silicon substrate, and to then evaluate the two generated Hall voltages in a suitable manner.
A drawback of the principle described above lies in the circumstance that of a magnetic field gradient has to be provided.
DE 43 00 605 C2 and U.S. Pat. No. 5,548,208 propose for said purpose, for example the U-shaped design of the current conductor through which the primary current to be measured is passed (FIG. 2). In both of said published documents, the actual magnetic field gradiometer is preferably applied to a carrier material separating the potential, said carrier material itself being secured on the U-shaped primary conductor.
However, the drawbacks of said principle are obvious: it is necessary to pass the current normally flowing in straight current conductors through a U-shaped primary conductor. For this purpose, massive current conductors or flat cables are interrupted especially in the high-current sector, and the conductor ends are connected in a suitable form to the connections of the U-shaped primary conductor. This method requires relatively much expenditure and it is difficult to reconcile it, most of all, with the manufacturing methods usually employed in the field of machine and vehicle manufacturing.
Therefore, an arrangement is known as well that permits with the use of at least two magnetic field measuring devices, measurements of the current without voluminous iron or ferrite cores in a manner that is relatively insensitive to homogenous fields of interference: in conjunction with DE 44 34 4177 A1, particularly two absolute-field measuring devices are arranged preferably on two sides of a straight conductor opposing each other (parallel with the direction of flow of the current) (FIG. 3). It is assured in this way that the circular magnetic field of the straight conductor penetrates the two measuring devices in the reverse direction. The output signals of both measuring devices are subtracted from each other, so that the interfering components of homogeneous interference fields are largely omitted.
Said invention, however, has inherent drawbacks as well. First of all, two magnetic field measuring devices and two potential-separating carrier substrates have to be used, as opposed to the gradiometric principle shown herein. Furthermore, the spacing between the two magnetic field measuring devices is not freely selectable because such spacing is particularly dependent upon the diameter of the primary conductor.
Said spacing, however, is decisive for the sensitivity of the arrangement to interference fields because the latter naturally change with the spacing. With simple mathematical means such as subtraction, the influences of said interference fields in the evaluation of the output signals of the absolute-field measuring devices can be minimized adequately only if such measuring devices are penetrated by approximately equal interference fields. When gradiometers are employed, the meaning of the term xe2x80x9cbasic width of the gradiometerxe2x80x9d, with respect to the sensitivity of said device versus interference fields, conforms to the spacing of the absolute-field measuring devices explained above.
The fact that the spacing between the absolute-field measuring devices is dependent on the cross section of the primary conductor in conjunction with DE 44 34 417 A1, is disadvantageous especially in the high-current area, which is characterized by both large primary conductor cross sections and high interference fields.
The invention eliminates the drawbacks of the two measuring methods described above, i.e. the use of a U-shaped primary conductor in conjunction with the gradiometric measuring method, and the predetermined base width in conjunction with the measuring method comprising at least two absolute-field measuring devices. A device and a method are proposed for said purpose that make it possible to measure current on a straight primary conductor either with the help of a gradiometer or with at least two absolute-field measuring devices, in a potential-free manner and with the elimination of external interference fields to a large extent.
Said problem is solved according to the invention in that
(a) the magnetic field gradient or gradients each are formed by a conductor that is provided with one or with a plurality of suitable recesses, for example grooves or slots, and which is preferably shaped straight in the site of the measurement; or
(b) formed by the correspondingly suitable arrangement of the conductive components forming in the site of measurement a preferably straight current conductor with one or a plurality of corresponding recesses;
and in that the magnetic field or the magnetic field gradient is measured in each case by suitable devices within the area surrounding individual recesses.
The invention permits measuring of the magnetic field gradient, for example in a groove located in a massive current conductor, said measure leads to a more compact structure and reduced manufacturing costs because the necessity of using the U-shaped design of the primary conductor is eliminated, as opposed to other gradiometer arrangements. Vis-à-vis the arrangements described above, which comprise at least two absolute field measuring devices that are arranged outside of a straight conductor, it has to be emphasized here that the realization possibility has more variability in particular for realizing base widths that are independent of the cross section of the primary conductor. It is possible in this connection to predetermine the desired base width based on the type of construction of the gradiometer employed, or to mount two or more absolute field measuring devices with the desired spacing from each other, and to then measure the magnetic field, gradient with the help of said measuring devices.
Furthermore, it can be assumed that the measurement of a magnetic field gradient located within the recess, or within its direct proximity, is afflicted with lower interference fields, to begin with, than the measurement of gradients or absolute fields located on the outside far removed from such a magnetic field gradient. At first, it seems to be difficult to explain said effect with the classic electrodynamics because the conductive materials forming the current conductor as defined by the invention can be expected to assure only screening against electrical fields, to begin with.
The addressed phenomenon, however, is measurable in a reproducible manner and can be attributed to eddy currents in the primary conductor that have a damping effect particularly on the changing outer fields causing such phenomenon.
A further aspect is added to the advantages offered hereinxe2x80x94which are predominantly of the physical typexe2x80x94from the viewpoint of manufacturing technology:
In conjunction with a device according to DE 43 00 605 C2, the accuracy with which the U-shaped primary conductor is positioned in relation to the actual magnetoresistive sensor element is highly significant as far as the measuring accuracy and the measuring range of the gradiometer are concerned. In analogy to said problem, the spacing and the symmetry of the absolute field measuring devices are critical values in conjunction with a device according to DE 44 34 417 A1, whereby additional expenditure is often required for adhering to said values.
A gradiometer or an arrangement of absolute field measuring devices capable of measuring magnetic field gradients are preferably produced by technical microsystem manufacturing methods, and such gradiometers or arrangements are often intergrated with the required evaluation electronics. In conjunction with modern methods for housing and encapsulating such microsystems, the mechanical manufacturing tolerances therefore can be kept within narrow limits.
Providing the primary conductor with a recess as defined by the invention, which recess can be produced, for example by milling a groove, is already possible with the means of classical machine building with an accuracy of a few hundredth parts of a millimeter as well. For joining the two components, only plug connections as commonly used in machine and vehicle building at favorable costs or manufacturing methods available at similarly favorable cost are then required, so that no additional measures are needed any longer for assuring the required positioning accuracy.
A further advantage of the invention lies in the possibility, for example for dividing high currents by multi-slot conductors in such a way that the gradients between the individual conductor currents will not become excessively large for measuring devices that are optimized for measuring smaller currents. Said advantage carries all the more weight in light of the fact that high unit numbers and thus relatively low manufacturing costs can be assumed to be feasible in current areas where multiple subdivision of the conductor is not necessarily required. In spite of said fact, a current conductor as defined by the invention can be useful with a plurality of recesses also when the signals of the measurement received within the area surrounding different recesses as defined by the invention are mathematically linked in a clever way. Interference fields can be suppressed in this way even more effectively than by recording a gradient.
As mentioned above several times, advantageous embodiments of the invention can be realized both with monolithically integrated gradiometers or with gradiometers integrated in same other way, as well as with suitable arrangements of absolute field measuring devices.
When using gradiometers it is necessary to take into account the direction of sensitivity of the areas of the gradiometer that are sensitive to the magnetic field. Especially in conjunction with a device according to DE 43 000 605 C2, it is advantageous if the sensor chip described in said cited published document is aligned in such a way that the base substrate of said sensor chip is inclined by about 45xc2x0 vis-à-vis the area that is put up by the direction of the flow of current and the center points of the cross sectional surfaces of the two conductor parts surrounding a recess as defined by the invention. It is assured in this way that the field lines will penetrate the magnetoresistive areas in a specially advantageous manner.
In conjunction with other magnetic field gradiometers capable of or operating on the basis of the GMR-, CMR- and Hall effect, or based on other magnetic field-sensitive effects, the approximately orthogonal alignment of the gradiometer in relation to said surface seems advantageous if only for technical manufacturing reasons alone. It seems to be possible also, of course, to build on the basis of the AMR effect a sensor whose magnetoresistive areas are shaped in, such a way that a straight alignment of the sensor becomes advantageous physically as well. Especially in conjunction with gradiometers operating based on the Hall effect, whose magnetic field-sensitive areas are applied to a base substrate in a planar way, an alignment of the base substrate parallel with the aforementioned surface seems to be advantageous. Irrespective of these considerations it seems possible to build with a major portion of the aforementioned effects gradiometers that can be physically arranged in the one or other way in the recess as defined by the invention, or in the area surrounding such a recess in an advantageous way, and in a manner that is favorable in terms of manufacturing technology as well.
Different arrangements are conceivable when arrangements of absolute field measuring devices and/or gradiometers are employed.
Advantageous arrangements of such measuring devices are explained in greater detail by way of example with the help of only one conductor provided having a recess as defined by the invention, in order to keep the scope of the following text within limits.
So as to able to exploit the advantages offered by said arrangements it seems to be advantageous, to begin with, if a straight number of magnetic field measuring devices or magnetic field gradient measuring devices of the same type of construction are symmetrically arranged in a groove as defined by the invention, or in the area surrounding such a groove, whereby the output signals of each of the respective measuring devices are linked within the area surrounding a recess by suitable mathematical operations such as, for example subtraction, and particularly linked in such a way that the interference components are minimized.
Furthermore, it may be advantageous also if such a measuring arrangement is put out of adjustment by suitable measures such as intentional asymmetrical mounting of such an arrangement in order to shift or expand the measuring range of the arrangement. Measures of said type seem to be particularly useful because the magnetic field gradient created in the recess as defined by the invention has a relatively low amount, as a rule:
A U-shaped current conductor is known to turn the direction of the flow of current by 180xc2x0. The means that the magentic field gradient in a plane located above the current conductor parallel with the base width of the sensor (see DE 43 00 605 C2 or FIG. 3) is often greater than the magnetic field gradient of an arrangement as defined by the invention, in conjunction with the same primary current.
Measures such as putting the magnetic field or magnetic field gradient measuring devices out of adjustment vis-à-vis the zero passage of the magnetic field can be flanked or compensated in a suitable manner by electronic measures, or through calibration.
The measures that may contribute to optimizing the magnetic flux in the area surrounding a recess as defined by the invention as well, comprise the arrangement of structural components made of materials capable of conducting the magnetic flux in a suitable manner. For example, the magnetic flux in the recess as defined by the invention is substantially increased if the conductor is partially enveloped with ferrite material. This measure, too, can be implemented both with the goal of optimizing the magnetic field gradient symmetrically in relation to the zero passage of the magnetic field, and for adapting it to the requirements of the application as well as of the measuring device, and with the intention of generating a field that is asymmetrical in relation to the zero passage.
For the purpose of realizing the last-mentioned intention, it is possible also to design the entire current conductor as defined by the invention in such a way that it is asymmetrical in relation to the recess in the direction of the current flow. Different currents or current flow densities occur in this way on both sides of the recess, which ensues the desired effect stated above.
Against the background of the state of the art in the field of microsystem technology such as, for example the flip chip technology, it is advantageous, among other things, if the gradiometers or magnetic field measuring devices are first secured on one or several carriers such as, for example foil carriers, and the microsystem so obtained is then positioned in the recess or within the proximity of the recess. A simple structure is realized in this way at favorable coat.
Another advantageous embodiment of the invention is based on the possibility that one or a plurality of magnetic field or magnetic field gradient measuring systems can be produced in such a way that such a system or such systems can be relatively exactly positioned or secured in the recess as defined by the invention. The relatively complicated positioning of the measuring systems in relation to the conductor is eliminated in this way, such positioning being normally required in order to assure exact measurements within an adequate measuring range.
Devices as defined by the invention provide the magnetic field gradients that are useful especially for the potential-free measurement of current, so that it appears to be advantageous in different current or temperature ranges or under the influence of other different environmental conditions if the measurements are carried out according to the method as defined by the invention, with the use of different magnetic field or magnetic field gradient measuring devices that operate based on a great number of different principles or effect.
The measured values so obtained; of course, often serve also for deriving or determining related values such as the voltage or the wattage.
Especially within the area of high currents, magnetic screening of the entire device or of part of the device may become necessary because of the occurrence of large interference fields, for example such as attaching additional metal parts, for example in the form of sheet metal, a vapor-deposited metal layer, or plastics containing metal particles and/or soft-magnetic materials, which in particular may be a component also of the magnetic field measuring devices themselves, for example of the sensor chips used and/or of the sensor microsystem and/or of the housing of the sensor arrangement, in order to screen such a device or a part thereof against external electromagnetic interference fields. Such a screening device can be realized with low expenditure owing to the extraordinary compactness of the measuring device.
In the presence of short-circuits or grounding, very high current flow already temporarily occurs in conjunction with devices rated for low currents. Such high currents can be easily detected by the method as defined by the invention. The output signals of the measuring devices can then be used, for example for monitoring purposes.
Owing to the compactness of the device and the possibility associated therewith for simple magnetic screening, the method is naturally particularly well-suited for detecting in a relatively confined space a plurality of currents with the help of a plurality of current conductors as defined by the invention.
Another possibility for measuring current at favorable cost ensues from the screening or screening capability as defined by the invention as well: when minimal interference fields can be expected to occur in the site where the magnetic field measured, or at the point of measurement of the magnetic field gradient when the invention is applied, it suffices if the measurement is taken only on one side of the zero passage of the magnetic field. Such a measurement can be carried out even with only an absolute field measuring device.
The preferably industrial prefabrication of the entire unit as a device for the potential-free measurement of current promises a substantial reduction of the unit cost. Units of said type can be particularly connected in a suitable manner at their conductor ends to the current conductors conducting the current to be measured. Particularly favorable in this connection are plug connections by which, for example flat cables can be connected to the units.
Another particularly advantageous way of manufacturing devices as defined by the invention can be expected to be of interest, for example in the field of automobile manufacturing:
In said field, the gradient-forming conductor as defined by the invention could be produced already as part of a final device.
Such a final device may be, for example a high-power generator, a conventional generator, a fuel cell or a fuse box. Components of said type are manufactured in very high piece numbers and consequently at relatively low cost. Furthermore, the realization of recesses as defined by the invention in the current conductors of such final device products can be expected to be possible at favorable cost as well. The devices suitable for measuring the created magnetic field gradients can then be supplied as prefabricated microsystems that are adapted to their application, and positioned in the area surrounding the recesses as defined by the invention.
Technical production measure of said type are, of course, advantageous in various forms of realization and can be expected to find use in different branches of industrial manufacture.
As mentioned above, the use of a conductor as defined by the invention comprising a plurality of recesses offers a number of various benefits. It is possible, first of all, to pass the primary current through the multiple slotting of the conductor in a way such that the measuring devices employed operate in their rated current ranges or rated field strength ranges.
A further advantage lies in the possibility for evaluating the various gradients: the values measured in the areas surrounding different recesses can be mathematically linked with each other in a manner that is suited for further minimization or elimination of the interfere components.
For the purpose of evaluating said signals as effectively as possible, it may be advantageous also if the measurement of the various magnetic field gradients is carried out by different methods.